1. Field of the Invention
The present invention relates to a lock mechanism for a valve timing regulation device which varies the opening and closing timing of one or both of an intake valve and an exhaust valve by an actuator in accordance with an operational condition of an engine.
2. Description of Related Art
A lock mechanism for a valve timing regulation device is known which is provided with a rotor and a housing able to rotate relative to a camshaft which opens and closes a valve of an engine system. The rotor and housing are synchronously rotated by locking them in response to engine operating conditions and are relatively rotated by releasing the lock.
FIG. 1 is a cross sectional view along an axial direction showing a lock mechanism for a valve timing regulation device in a first conventional example as disclosed for example in JP-A-9-280018. In the figure, reference numeral 1 denotes a camshaft which drives the opening and closing of a valve in an engine system and 2 is a timing pulley which is rotatably attached on the camshaft 1. A rotational driving force is transmitted from a crank shaft (not shown) of the engine to the timing pulley 2. 3 is a housing which is fixed to rotate integrally with respect to the timing pulley 2. 4 is a rotor which is linked to a tip of the camshaft 1 and which is stored in the housing 3. The rotor 4 has a plurality of vanes 4a which extend in a radial direction and slidably abut with a side of the timing pulley 2 and an inner peripheral surface of the housing 3. The rotor 4 can rotate relatively to the housing 3. 5 is a cover which covers the open end of the housing 3. 6 is a through hole which is provided on one vane 4a of the rotor 4 and which extends in an axial direction of the camshaft 1. 7 is a locking hole which is provided on the timing pulley 2 and which is communicated with the through hole 6. 8 is a lock pin which is slidably inserted in the through hole. The lock pin 8 is urged by a spring 9 and is inserted into the locking hole 7. The housing 3 and the rotor 4 are locked by the insertion of the lock pin 8 into the locking hole 7, thereby to prevent the relative rotation of them. 10a is an oil passage which is connected to the locking hole 7, 10b is an oil passage which is connected to the large diameter hole 6a of the through hole 6. The oil passages 10a, 10b are connected to an oil pressure supply means (oil pump) through an oil control valve (not shown). When an oil pressure supplied to the large diameter hole 6a of the through hole 6 and the locking hole 7 from each oil passage 10a, 10b increases to above a predetermined value, the locking pin 8 releases the lock of the rotor 4 and the housing 3 by retracting from the locking hole 7 by the oil pressure against the urging force of the spring 9.
The operation of the first conventional lock mechanism for a valve timing regulation device will be discussed below.
When the engine is stopped, the oil pressure applied to the locking pin 8 is not more than the predetermined value, the locking pin 8 on the rotor side is engaged with the locking hole 7 of the timing pulley 2 by the urging force of the spring 9. Thus, the rotor 4 and the housing 3 integrated with the timing pulley 2 are in a locked state. After this state, when the oil pressure supplied to the large diameter section 6a of the through hole 6 and the locking hole 7 through the oil passage 10a, 10b exceeds the predetermined value by the activation of the oil pump due to engine startup, the locking pin 8 retracts from the locking hole 7 by the oil pressure resisting the urging force of the spring 9. In this way, the lock of the rotor 4 and the housing 3 is released and these components can undergo relative rotation. As a result of this relative rotation, the opening and closing timing of the valve is regulated.
Since the first conventional lock mechanism for a valve timing regulation device is constructed above, it is necessary to store a locking pin 8 in the vane 4a (through hole 6) of the rotor 4 to slide along the axial direction of the camshaft 1. The vane 4a storing the locking pin 8 must be formed to be longer in the circumferential direction in comparison with other vanes which do not store the locking pin 8. When the length in the circumferential direction is lengthened, not only is the regulated angular range of the valve timing regulation device reduced, but also the balance with respect to the center of rotation of the rotor 4 is lost. Thus, problems with respect to mechanical strength and the generation of vibrations have arisen.
FIG. 2 is a cross sectional view in the radial direction of a lock mechanism for a valve timing regulation device according to a second conventional example as disclosed for example in JP-A-9-303118. Those components which are the same or similar to components in FIG. 1 are denoted by the same reference numerals and further discussion will be omitted. In FIG. 2, reference numerals 3a, 3b are shoes which protrude from the inner peripheral surface of the housing 3. Of the shoes 3a, 3b, one shoe 3a is formed to be longer in the circumferential direction than the other shoe 3b in order to store the lock mechanism. 11 is a pin hole which is provided on the shoe 3a and extends in a radial direction of the housing 3. 12 is a locking pin which is inserted slidably in the pin hole 11. 13 is a spring which urges the locking pin 12 in a direction of the rotor 4. 14 is a locking hole provided on the rotor 4. The locking hole 14 is connectable with the pin hole 11. 15 is an oil passage which is connected with the locking hole 14. An oil pressure from the oil pressure control system is supplied to the oil passage 15.
The operation of the second conventional lock mechanism for a valve timing regulation device will be discussed below.
The locking pin 12 on the housing 3 side is inserted into the locking hole 14 of the rotor 4 by the urging force of the spring 13, the housing 3 and the rotor 4 are locked to rotate synchronously. When the oil pressure supplied to the oil passage 15 in response to an operational condition of the engine exceeds a predetermined value, the locking pin 12 is displaced towards an outer peripheral surface of the housing 3 by the oil pressure against the urging force of the spring 13 and the locking pin 12 retracts from the locking hole 14. In such a way, in the same way as the first conventional example, the locking of the rotor 4 and the housing 3 is released and both components are retained in a state allowing relative rotation.
Since the second conventional lock mechanism for a valve timing regulation device is constructed above, of the shoes 3a, 3b of the housing 3, it is required to make the shoe 3a which acts as storage for the lock mechanism to be longer in the circumferential direction than the other shoe 3b. When the length in the circumferential direction is lengthened, in the same way as the first conventional example, not only is the regulated angular range of the valve timing regulation device reduced, but also the balance with respect to the center of rotation of the rotor 4 is lost. Thus, problems with respect to mechanical strength and the generation of vibrations have arisen.